(1) Field of the Invention
The present invention relates generally to an apparatus for filling receptacles with precise amounts of particulate material from a continuous stream of such material moving along a pathway, and in particular to an apparatus for controlling the speed at which the receptacles are fed into the pathway responsive to the measured amount of material being fed along the pathway.
(2) Description of the Prior Art
Numerous solid particulate materials are packaged in various types of containers for sale to the ultimate consumer or to a downstream processor. A brief exemplary listing of such materials include plastic and metal components and parts; food items, such as cereals, corn meal, rice, spices, soybeans, and potato chips; and a variety of other materials, such as tobacco, plastic pellets, etc. Exemplary containers include boxes, containers, pouches, packages, cartons, and bags.
Generally, the material is fed as a continuous or discontinuous feed from a bulk supply source, such as a hopper, directly into the containers or into intermediate collection hoppers for transfer into the containers. The apparatus used to transfer the material from the supply source into the individual receptacles, the term being used herein to encompass both the final containers and intermediate hoppers or other temporary material holders, may vary dependent upon the type of material, but will normally include a means for weighing the material at some point between the supply source and the receptacle or within the actual receptacle, with some feed-back being provided to control the feed rate, and thereby the amount of material being fed into a given receptacle during a given time period. Control of the feed rate is used not only for material packaged by weight, but also for items packaged by the number of items, since these latter items are frequently packaged on the basis of the weight of the number of items in a container, as opposed to counting the number of items packaged.
In some types of apparatus used to discharge material into a plurality of receptacles, a continuous stream of the material is fed from a bulk supply source, such as a bulk hopper onto a weigh conveyor, and then discharged from the conveyor along a first pathway into a first receptacle. The weight of material conveyed into the first receptacle is measured, either by weighing the amount of material being conveyed, or the weight of the receptacle. When the desired weight is reached, the material stream is directed into a second receptacle. In many instances, a weigh conveyor is used to measure the weight of material being carried on the conveyor during a given time, thereby indicating the weight of material fed to the receptacle.
For production efficiency, some materials are fed continuously at a high rate of feed, with up to the order of 600 containers per minute being filled. Unfortunately, existing filling systems do not measure the material with a high degree of accuracy, particularly at these higher feed volumes. As a result, the amount of material in different receptacles may be more or less than the target amount. Normally, manufacturers overfill containers by an amount sufficient to ensure that the stated weight is met, with a corresponding increase in manufacturing cost. Therefore, there is a continuing need for an apparatus for accurately dispensing solid particulate material from a bulk supply source into a plurality of receptacles, either the final containers or intermediate receptacles, based on the weight of the material being dispensed.
The present invention addresses this need by providing an improved apparatus for continuously and accurately weighing a continuous stream of solid particulate material, and rapidly adjusting the speed at which receptacles are conveyed into the stream. Generally, the present invention is comprised of a dynamic measurement device to continually measure the weight of material being fed along a pathway, a receptacle conveyor to carry consecutive receptacles into the pathway for filling, and control circuitry to rapidly adjust the speed of the receptacle conveyor in response to measurements by the measurement device. The apparatus may also include means to control the rate at which material is fed to the measuring device responsive to weight or material flow measurements.
Particularly suitable dynamic measurement devices are described in earlier U.S. Pat. Nos. 5,219,031, issued Jun. 15, 1993, and U.S. Pat. No. 5,230,251, issued Jul. 27, 1993, to the present inventor, both patents being incorporated herein by reference in their entireties. Generally, the dynamic measurement device is comprised of a curved weigh pan having inlet and outlet ends, and an inwardly curved surface extending between the pan ends. The pan is positioned to receive a continuous stream of solid particulate material tangentially at the inlet end, i.e., the material stream is directed substantially perpendicular to the radius of curvature of the pan at the upper end. As a result, the material flows around the curved surface of the pan without impacting the pan, eliminating errors due to the movement of the pan under impact forces.
The pan is mounted on the distal end of an elongated support arm, with the proximal end of the arm being attached to a suitable support at a distance from the pan. To permit pan displacement, the arm is either flexible or is pivotally attached at its proximal end. When material flows over the inwardly curved pan, an inward centripetal force, and a corresponding outward force, is exerted causing the pan to move outwardly. This outward movement, corresponding to the weight, or change in weight, of the material moving across the pan is measured by the displacement measurement instrument. A displacement measurement instrument, such as a transducer, is positioned to continuously measure the displacement of the pan. Thus, a dynamic measurement device is capable of measuring variations in the amount of material moving along a given pathway without interrupting the flow of material.
Since the outward force exerted against the pan is due entirely to the centripetal force, and is independent of any impact or frictional forces, measurement is highly accurate, and can be measured instantaneously and continually. For optimal measurement independent of non-centripetal force factors, the pivot point of the arm is preferably located so that a line extending from the arm to the pan approximately midway between the pan inlet and outlet ends is perpendicular to the radius of curvature of the pan. In the present apparatus, the dynamic measurement device is positioned to receive material fed tangentially along the inner surface of the pan at its inlet end.
A receptacle conveyor is positioned downstream of the measuring device to carry consecutive receptacles into the pathway of the material discharged from the exit end of the measurement device. Each receptacle is filled with a predetermined amount of falling material as the receptacle moves thorough the pathway. Upon filling of a given receptacle with the desired amount of material, the continually moving conveyor carries the next receptacle into the material pathway.
The amount of material entering a given receptacle is thus dependent on the weight of material moving along the pathway and the length of time that the given receptacle intersects the pathway. Therefore, by continuous determination of the amount of material flowing along the pathway, and knowing the desired target receptacle content, the correct amount of material can be fed into a given container by adjusting the speed of the receptacle conveyor, and thereby the time that a given receptacle is in the pathway.
In order to ensure precise filling of a given receptacle, certain conditions should be met. First, the receptacle conveyor should be positioned downstream of the pan discharge end so that the receptacle fill openings will be proximate to the discharge end of the measurement device, e.g., within about 2 feet, normally within 0.5 to 1.5 feet. If so, the amount measured at a given time will approximate the amount of material entering the receptacle at that time. Second, the speed of the conveyor must be adjustable within a short period of time, e.g., within about 100 ms, and preferably within about 20 ms after receiving a control signal. Generally, a servo will be used to achieve this desired rapid response, although other conveyor adjustment means will be apparent to one skilled in the art.
Generally, a transducer or other continuous displacement measurement instrument is used to measure displacement of the pan. A controller or processor then receives displacement information from the transducer or other displacement measurement instrument, and calculates the weight of material being fed over the pan. A control signal is then sent to the conveyor speed control means, e.g., a servo, resulting in an increase or decrease in conveyor speed, thereby controlling the period of time a given receptacle intersects the pathway ensuring precise filling of the receptacle.
The above receptacle conveyor control mechanism may be used alone or combined with a material feed control mechanism. When combined in this manner, the receptacle conveyor control mechanism is used to provide precise adjustments as described above, while the material feed control mechanism is used to provide relatively slower, greater adjustments in the volume of material being fed across the displacement measurement instrument. Essentially, the feed control mechanism is comprised of a material flow control means that is adjustable to increase or decrease the flow of material, with the flow control means being adjusted in response to a signal received from the controller based on the weight of material flowing past the displacement instrument. The flow control means may be, for example, a feed conveyor drive means, or a valve on a feed hopper.
When used together, the displacement instrument continually measures the weight of material being fed along a material pathway. The measured weight is fed to a controller that calculates the desired speed of the receptacle feed based on the known target weight of material to be placed in the receptacle. The controller then sends a speed adjustment command to the receptacle conveyor drive mechanism to increase or decrease the conveyor speed to maintain the amount of material being fed into a receptacle on target. The controller can also send a control signal to the flow control means, e.g., if the speed at which receptacles are fed into the material pathway varies outside of a desired range of receptacles per minute.